The company’s Nook HD and Nook HD+ are credible content-consumption tablets — remarkably credible, actually, considering that they come from a 127-year-old bookseller. But they sold so poorly over the holiday season that it raised questions about whether B&N would end up being forced to de-emphasize its hardware business in favor of selling content on other platforms.

The Nooks use Barnes & Noble’s own custom version of Android and provide its own stores for books, magazines, newspapers and apps. And therein lies an oft-raised argument against buying a Nook: the Barnes & Noble application store has had only 10,000 pieces of software — mostly for-pay ones — vs. the hundreds of thousands of choices in Google’s Google Play.

So with one fell swoop, in the form of a software update being rolled out today, B&N is eliminating that downside. It’s giving both Nooks the Google Play stores for apps, music, movies and books, plus key Google apps which the tablets have lacked until now: Chrome, Gmail and YouTube. (Google’s policies for its apps are an all-or-nothing proposition for device makers — if they want Google Play, they also have to pre-install Google’s apps.) New Nooks sold at Barnes & Noble’s bookstores and elsewhere will also carry the updated software.

The bottom line: if something’s available for Android, it’s now available for Nook, assuming it’s compatible from a technical standpoint. Among other things, that means you’ll be able to install Amazon’s Kindle app on a Nook and read books you’ve purchased from Amazon. For the first time, the notion of someone with a heavy investment in Kindle books buying a Nook doesn’t sound completely impractical.

Apps you bought from Barnes & Noble will be marked with an “n” label (for Nook). And if you’ve bought Google Play apps for another Android device, they’ll be downloaded to your Nook at no extra charge.

The arrival of the standard Android stores and apps doesn’t mean that the Nooks are becoming plain-vanilla, general-purpose Android devices. They still sport Barnes & Noble’s heavily-customized version of Android 4.0 Ice Cream Sandwich, with a reading-centric home screen and B&N’s own services and apps for books, magazines, newspapers and video. (It hasn’t had a music store of its own.) The fact that the tablets don’t run Android 4.2 Jelly Bean, the latest version of the operating system, is largely moot: B&N has modified the software’s look and feel so much that it’s not readily apparent which flavor of Android its devices run.

Stephane Maes, vice president of product for Barnes & Noble, told me that the company will continue to operate its own application store. But with Google Play on its devices, it won’t be under pressure to be comprehensive. Instead, it can focus in on particular categories, such as high-quality kids’ software.

All of this adds up to one gigantic, gutsy gamble for Barnes & Noble. It’s been selling its tablets at dirt-cheap prices — $199 for the 7″ Nook HD, and $269 for the 9″ Nook HD+ — in hopes of turning an overall profit by selling content. Starting today, you could buy a new Google-ized Nook at the same price and buy all your content through Google’s stores rather than from Barnes & Noble.

Maes told me that the company understands the risk. But “we’ve done a lot of analysis,” he says, “and while we may lose some sales to Google, a rising tide carries all ships.” In other words, it hopes to sell a lot more Nooks, thereby giving it a lot more customers for its content. (And B&N’s own stores remain hardwired into the Nook interface in a way which Google Play will not be.)

I wasn’t even sure whether what Barnes & Noble is doing was technically possible on devices with interfaces that depart so sharply from standard Android. But it is, and it’s hard to see any reason why this isn’t good news for Nook owners and potential Nook owners. It also draws a sharper distinction between the Nook and Amazon’s Kindle Fire tablets, which don’t have Google’s stores and offer no straightforward access to Google’s apps.

It’s way too early to know whether B&N’s gambit will help end the Nooks’ sales doldrums, but it’ll be fun to watch — and offhand, I can’t think of any other strategy with better odds of paying off.

Oh, and one odd side note. Microsoft is part owner of the Nook business, having invested $300 million in it. As part of its ongoing, Google-bashing “Scroogled” campaign, the company is currently telling consumers that they should find Google Play’s policy of sharing users’ names, e-mail addresses and zip codes with developers of paid apps to be deeply unsettling. The whole campaign is a counter-productive embarrassment, and I can’t wait until Microsoft figures that out. But I wonder how the company feels about the fact that products it owns a piece of will be, um, Scroogling people?